Tropical Storm Barry was poised to make landfall Saturday as the first Atlantic hurricane of 2019, with heavy rain and strengthening winds near Louisiana’s shore.

The U.S. Coast Guard said it was trying to rescue a dozen people stranded on a remote Louisiana island by flooding. Petty Officer Lexie Preston said some of the people were on rooftops on the Isle de Jean Charles, about 70 kilometres south of New Orleans.

The storm was packing maximum sustained winds of 115 km/h and was on track to reach hurricane strength around noon local time as it crosses the Louisiana coastline southwest of New Orleans.

The storm is expected to weaken after it moves inland.

The NHC said rainbands from the system began to move onshore early Saturday. Meteorologists have warned that torrential rain — as much as 60 centimetres in some places — could unleash severe flooding.

U.S. National Hurricane Center director Ken Graham said Barry is gathering “a big slough of moisture.” He delivered a storm update using Facebook Live from the hurricane centre, where he pointed to a computer screen showing a big swirling mess of airborne water.

Employees remove a sign in the French Quarter as Tropical Storm Barry approaches land in New Orleans, La., July 12, 2019. (Jonathan Bachman/Reuters)

“That is just an amazing amount of moisture,” he said. “That is off the chart.”

Graham said the storm is moving so slowly that heavy rain will likely continue throughout the weekend across Louisiana. He reminded viewers that “83 per cent of fatalities from these systems have been from inland rain. So let’s stay off the roads. Let’s prevent these preventable fatalities.”

According to Entergy Louisiana’s outages map, more than 45,800 people have been affected by power outages. Nearly a fourth of those outages were in coastal Terrebonne Parish. A number of other southern parishes were affected, including Jefferson Parish outside of New Orleans.

Those parishes were east of Morgan City, about 110 kilometres southwest of New Orleans, where Barry is expected to make landfall as a hurricane.

Tracking forecasts showed the storm moving toward Chicago, swelling the Mississippi River basin with water that must eventually flow south again.

The U.S. National Hurricane Center released this satellite image of the storm on Saturday. (U.S. National Hurricane Center)

Officials from the U.S. Army Corps of Engineers, which maintains the levees, have insisted that no significant breaching of the six-metre-high levees in New Orleans was likely.

The brunt of Barry’s force was expected to skirt the western edge of New Orleans, avoiding a direct hit on a low-lying city virtually surrounded on all sides by rising waters.

But Mayor LaToya Cantrell said 48 hours of heavy downpours could overwhelm pumps designed to purge streets and storm drains of excess water.

“There is no system in the world that can handle that amount of rainfall in such a short period,” Cantrell said on Twitter.

U.S. President Donald Trump declared a state of emergency for Louisiana on Friday, freeing up federal disaster assistance if needed.